D3 SL Reproduction, menstrual cycle

Asexual reproduction

A form of reproduction that involves only one parent and produces offspring that are genetically identical to the parent. Allows to produce a large number of offspring in a short period of time, and is less complex and energy-requiring. Chances of genetic variation are low.

Sexual reproduction

A form of reproduction that involves the fusion of male and female gametes to form a zygote, resulting in genetically diverse offspring. This is a more energy-requiring and complex form. This results in genetic variation, thus the species are more better adapted to environmental changes.

Causes of genetic variation during meiosis

Crossing-over in prophase I, Random orientation of homologous chromosomes into pairs in metaphase I, fusion of random gametes in fertilisation.

Hermaphrodites

Organisms that have both male and female reproductive organs.

Gametes

Haploid sex cells (sperm and egg in animals; pollen and ovules in plants) that are formed by meiosis and are used in sexual reproduction to form a zygote upon fertilization.

Zygote

A diploid cell formed by the fusion of two haploid gametes during fertilization. It is the first cell of a new individual.

Sperm

The male gamete in animals, which is haploid, small, motile, and millions of it is produced by testes every day. During sexual reproduction, it must travel up the female reproductive tract to fuse with the egg and deliver paternal DNA.

Eggs/ova

The female gamete in animals, which is haploid, large, and immotile. It carries food reserves that act as energy source for the dividing zygote. It is produced in ovaries and only one egg is released per menstrual cycle in humans.

Sperm ducts

Tubes through which the sperm travels from the testes to the urethra during ejaculation.

Prostate glands

Glands that produce fluids that help in the transport and nourishment of the sperm. The sperm together with these fluids is called semen.

Semen

A slightly alkaline fluid containing sperm and secretions from accessory glands (such as the seminal vesicles, prostate gland, and bulbourethral glands) that is ejaculated from the male reproductive system during sexual intercourse.

Urethra

A common tube from which both the sperm and urine leave the penis.

Penis

A muscular erectile organ that helps in the transfer of the sperm from the male reproductive system to the vagina.

Seminal vesicles

Vesicles that produce fluids that help in the transport and nourishment of the sperm.

Epididymis

Highly coiled tubes where sperm mature and are stored until the time of ejaculation.

Scrotum

Sacs that hold the testes and maintain them at temperature 2-3C lower than the body temp, facilitating sperm production.

Testes

Two small organs that produce sperm and testosterone.

Bulbourethral glands

Glands that produce fluids that help in the transport and nourishment of the sperm.

Uterus

A muscular, hollow organ in the female reproductive system where a fertilized egg (zygote) implants and develops into an embryo and fetus during pregnancy.

Ovaries

Organs that produce eggs and female hormones oestradiol and progesterone.

Oviducts/fallopian tubes

Tubes through which the egg (ovum) travels from the ovaries. Fertilisation occurs here.

Cervix

Lower part of the uterus. Menstrual blood passes from the uterus to the vagina through this place. It widens during childbirth.

Vagina

The muscular canal in the female reproductive system that serves as the site for sperm entry during sexual intercourse and the birth canal during childbirth.

Menstrual cycle

The monthly series of changes the body goes through to prepare for pregnancy due to variation in the levels of ovarian and pituitary hormones.

Ovarian cycle

Cyclic changes seen in the ovaries during menstrual cycle which include: follicular phase, ovulation, and luteal phase.

Follicles

Small sac-like structures in the ovaries that contain oocytes.

Follicular phase

Phase of the ovarian cycle that starts form the first day of menstruation up to ovulation. The follicles start growing, producing oestradiol. Rising oestradiol helps rebuild the uterine lining and signals to reduce FSH levels. A surge of oestradiol (which happens after the dominant oocyte is chosen which keeps producing high levels of oestradiol) triggers the rise in LH levels, leading to ovulation.

Oestradiol

A type of estrogen hormone produced primarily by the ovaries during the menstrual cycle. It is involved in the development of secondary sexual characteristics and the regulation of the menstrual cycle, including thickening of the uterine lining, and maturation of the egg.

Progesterone

A steroid hormone produced by the corpus luteum and later by the placenta during pregnancy. It prepares the endometrium for implantation of a fertilized egg and helps maintain pregnancy.

LH

A hormone produced by the anterior pituitary gland. It plays a key role in regulating the menstrual cycle, particularly in ovulation. It triggers the release of a matured egg from the follicle and stimulated the formation of corpus luteum.

FSH

A hormone produced by the anterior pituitary gland. It is essential for the development and maturation of follicles in the ovaries.

Ovulation

Phase of the ovarian cycle that occurs after the follicular phase. A large surge of LH (caused by high oestradiol from the dominant follicle) causes the mature follicle to release the egg.

Corpus luteum

A temporary structure that forms in the ovary after ovulation from the remnants of the ruptured follicle. It secretes progesterone (and some oestradiol) to maintain the endometrium in preparation for a potential pregnancy.

Luteal phase

Occurs from the end of ovulation to the start of the next menstruation. The rupruted follicle transforms into corpus luteum, which produces a lot of progesterone and some oestradiol. Progesterone stabilizes and thickens endometrium, preparing it for a possible pregnancy. If no fertlization occurs, the corpus luteum degenerates, thus progesterone and oestradiol levels fall and menstruation begins again.

Uterine cycle

The changes that occur in the uterus during menstrual cycle which can be divided into: menstruation, the proliferative phase, and the secretory phase.

Proliferative phase

Phase of the uterine cycle which coincides with follicular phase. Oestradiol secreted by the growing follicle causes thickening of the uterine lining, preparing for a potential pregnancy.

Secretory phase

Phase of the uterine cycle that roughly coincides with luteal phase. Due to high levels of progesterone, the uterine lining thickens further and turns into a secretory layer, in preparation for a potential implantation of a fertilized egg.

Menstruation

Phase of the uterine cycle where the decrease in FSH and LH levels causes corpus luteum to break down. The subsequent decrease in progesterone and oestradiol causes the thickened lining of the uterus to break down. The broken down layers, the unfertilised egg, and blood are shed from the body through the vagina, resulting in menstrual bleeding.